EP1142981A2 - Apparatus for power generation by gasification of biomass with subsequent catalytic removal of tar compounds from the heating gas - Google Patents

Abstract

Lower isoparaffins are synthesized by: (a) stage 1: synthesizing straight chain hydrocarbons by contacting the synthesis gas with a Fischer-Tropsch synthesis catalyst; and (b) stage 2: synthesizing isoparaffins in by contacting the straight chain hydrocarbons synthesized in the first stage, with a mixture of hydrogenation catalyst or solid acid catalyst. Synthesis of lower isoparaffins from synthesis gas that is a mixture of hydrogen and carbon monoxide involves: (a) stage 1: synthesizing straight chain hydrocarbons by contacting the synthesis gas with a Fischer-Tropsch synthesis catalyst; and (b) stage 2: synthesizing isoparaffins in by contacting the straight chain hydrocarbons synthesized in the first stage, with a mixture of hydrogenation catalyst or solid acid catalyst for hydrocracking and isomerizing the straight chain hydrocarbons.

Description

Technical application area

The technical field of application extends to a device for the thermochemical gasification of carbon-containing solid fuels, in particular biomass, with the purpose of using the fuel gases generated in the gasifier for power generation, in particular by means of internal combustion engines (for example gas engines). This is usually done first by converting chemical energy into thermal energy, which does work in an engine and thereby generates mechanical energy (rotational energy), which in turn drives an electrical generator. The power range of the power generation plants is typically 50 to 5000 kW _el .

The inventive design of the device allows the To operate gas generation downstream process units without the the gasification as a by-product of tar compounds Cause malfunctions. This is achieved through a selective catalytic Splitting the tars into usable fuel gas.

In this context, the term tar is all about gasification emerging hydrocarbons taken, which when cooling the gas to the for the use of the necessary temperature leave its gaseous state and which goes hand in hand with this change in properties the overall process in permanently disrupt its function.

State of the art

The thermochemical gasification of biomass creates flammable materials Commercial gas also a mixture of condensable or sublimable Hydrocarbons (tars) that are produced at the high temperatures of gas production (> 700 ° C) in vapor form in the gas. For the use of the fuel gas in Units that serve the purpose of generating electricity must have the fuel gas to be cooled, causing it to condense or resublimate the tars is coming. This makes downstream process units strong in their function impaired. Therefore, in order to make the fuel gases usable for this application extensive elimination of the troublesome by-products (tars) is required.

The tar components created during biomass gasification settle mainly from gaseous simple and complex, mostly polycyclic, aromatic hydrocarbons with molar masses of up to 300 g / mol together. With regard to the suitability of a fuel gas for electricity-generating use, the It is important to minimize those components that start with the cooling of the gas Condense or resublimate at 300 ° C.

For the resulting need for tar disposal exist different procedural approaches, the different good but seen overall can realize insufficient gas qualities. In addition, there are some The high costs for investment and / or operation that the Make the entire process economically unattractive.

When generating gas in a fixed bed or moving bed, in the case of large-scale biomass under the influence of gravity in the mass flow a gasification shaft from the top to the top wandering below while gassing slowly, i. w. two Basic principles differentiated. Countercurrent gasification is comparative technically simple and undemanding, but produces fuel gases with extremely high Keep tar.

On the other hand, with the technically more demanding direct current gasification, it is possible to produce sufficiently good quality for electricity generation, at least with small units of fuel gases. This is achieved through a hot glowing zone that flows through the tar-containing gas before it leaves the carburetor. The tar compounds on the hot surfaces of the coke particles are largely split. In systems> 50 kW _el or associated gasification units> 200 kW _th , it becomes increasingly difficult to move the fuel bed in a steady flow, so that in larger systems tars are found in the product gas in too high a concentration.
Constructive variations of the two basic types of fixed bed gasifiers also do not convincingly solve the tar problem, so that a subsequent tar treatment stage is generally indispensable.

When generating gas in fluidized bed systems, it is possible to Pyrolysis process, by adding catalytically active additives directly into the bed material to lower the tar contents in the product gas. In different Such procedures have been described in work (SIMELL 1992, OLIVARES 1997). However, these procedures are not sufficient to Quality requirements of the fuel gas for use in electricity generation fulfill.

A circulating downstream of the gasification plant as a tar treatment stage Fluidized bed in which the tar-laden gas is at a high temperature level catalytic dolomite is brought into contact, achieves high gas qualities, the investment and operating costs required, however, enormous is high (RENSFELT 1997).

The tar removal from the fuel gas by gas scrubbing corresponds to Contrary to the flue gas scrubbing in power plants is not the state of the art and is especially impractical because of the high investment and operating costs (THOME-KOZMIENSKY 1985, BORN 1998). The tar separation from gases through Gas scrubbing or watery quenches is primarily known from coking technology, the tar concentrations being several orders of magnitude higher than in biomass gasification and also the requirements for gas purity are much lower. The disadvantage of gas scrubbing processes in terms of The energetic utilization of the biomass used also results in the loss of Calorific value of the separated hydrocarbons.

Methods are often described in which the gas purification by means of a Gas generator downstream fixed bed reactor takes place (ORIO 1997, SIMELL 1994, ALDEN 1988). The product gas is here by a catalytically active Particles existing fixed bed directed. Usually more in practice or less heavy dust loading of the product gas, however, it occurs Contamination and blockage of the fixed bed reactor and thus blockages and deactivating the catalytically active components. A cleaning and regeneration of the fixed bed catalysts during operation is difficult perform.

DE-OS1542624 describes a process for the catalytic cleavage of known gaseous hydrocarbons, in which the gases through an annular Catalyst bed are passed through, with an external heating through integrated burner.

EP0360505 is an apparatus for reforming hydrocarbons known, the gas through different reforming catalyst beds is passed through and heating by a centrally arranged burner he follows.

An endothermic reactor for gas processing is known from JP60235634, in which the hydrocarbon-containing gas through a plurality of catalyst layers contained pipe is passed.

DE4430645 describes a reactor for the catalytic conversion of exhaust gases, especially known for exhaust gases from internal combustion engines. Here will the exhaust gas flow is catalytically arranged in a metallic jacket acting honeycomb body.

DE 19721630 describes a device for reforming hydrocarbons known, which consists of a radiant burner and a reforming reactor, which Can contain metal honeycomb body with a catalyst coating, put together. With the help of the device, especially small Performance range of hydrocarbon-containing gases converted into synthesis gases become.

Presentation of the invention

The invention is based, so the known devices the task change that the fuel gas to be used to generate electricity is only so contains small amounts of condensable hydrocarbons (tars) that a trouble-free operation of the generator is permanently possible. Furthermore the device according to the invention provides a method for gas conditioning Available, which is also justifiable from a business point of view is.

If a corresponding purity of the fuel gas is ensured, this can be done in suitable downstream units (e.g. gas engine, gas turbine, Stirling engine, Fuel cell, etc.) are used for energy conversion, and it arises in this way an advantageous process engineering process for direct electricity generation of the regenerative energy source biomass.

Due to integrated components for cleaning and regeneration of the catalytically active material becomes a continuous process operation enables.

Appropriate measures are taken to ensure that crack reactions occur Deactivation can be largely avoided.

In conventional devices, the gas generator is directly introduced Coming gas in a power generating unit is not possible because the gas Condense the tars contained in the power generator and create a trouble-free one therefore do not allow continuous operation. So they have to be in the gas contained tars in a process stage upstream of the power generator the fuel gas are removed. These requirements are met by the device according to the invention fulfilled.

The conventional devices are often limited to a narrow performance range limited. The inventive device can be changed by Use device dimensions in a wide range of services.

In the device according to the invention, the process stages of the Fuel gas generation (gasification) and the use of fuel gas (e.g. gas engine, Gas turbine, fuel cell, Stirling engine and. a.) a suitable process level in Intermediate form of an advantageously designed catalyst stage, which the tar compounds largely removed from the gas (see Fig. 1).

The tars are removed within the catalyst stage by use one or more special catalytically active materials that cause the cleavage catalyze the tar. In the presence of the catalytic surfaces, the Tar compounds through chemical reaction with other gas components in split smaller molecules, which increase the calorific value of the gas.

This is done through the use of a catalytically active material, which tars in the gasification reactor (hydrocarbons of the general composition C _n H _m ) in the temperature range from 700 ° C to 1000 ° C with parts of the main gas components according to the following reaction equations into the combustible gases CO and H ₂ chemically converted (catalytic reforming): C _n H _m + n H ₂ O  n CO + (n + m / 2) H ₂ C _n H _m + n CO ₂  2n CO + (m / 2) H ₂

The device for removing the tars from the biomass gasification product gas produced by catalytic cleavage is technically such formed that the gas is passed through it with a suitable dwell time and which contains catalytically active material. The carrier-fixed The catalyst material is in a channel-shaped configuration on a support frame in a thermally insulated container installed, the channels parallel to Flow direction. The channel cross sections are chosen to be as small as possible, by small mean free path lengths for the gaseous or vaporous Realize tar components and thus the contact of the gases with the Ensure catalyst area. The parallel arrangement of many such channels results in a honeycomb structure.

Devices for cleaning and Regeneration of the catalytically active material. By adding suitable gaseous or vaporous substances with the help of injection devices, can flushing and regeneration of the catalyst can be achieved. This will an impairment of those that come into contact with the product gas Catalyst surfaces due to dust and carbon-containing deposits avoided. The inventive design of the device therefore allows the use of the device even with dusty product gases. Through periodic Application of the cleaning measures during operation is a Deactivation of the catalyst by superficial solid deposits prevented.

Furthermore, according to the invention, the possibility of injection within the Partial oxidation can be performed.

Embodiment

An embodiment of the method on which the device is based is shown in Figure 2 (process diagram) reproduced.

Biomass wood is used as an example of raw material. The wood will in a continuous process in a fluidized bed gasifier using the Gasification medium air converted to fuel gas. The process takes place in a swirling sand bed at temperatures of approx. 900 C. After leaving of the gasifier, the hot raw gas is passed through the catalytic reformer where the tar compounds contained in the gas are split. The fuel gas will then cooled to approx. 60 ° C, filtered and fed to a gas engine, which drives an electric generator.

FIG. 3 shows an embodiment of the catalytic device Tar splitting (catalytic reformer).

The hot raw gas enters the reactor through a pipe socket 1 , which is formed by a container 4 and a thermal insulation 5 . One or more levels with the honeycomb catalysts 7 are arranged within the reactor, each of which is held by a supporting structure 6 . On the upstream side of the honeycomb body 8 an upstream device 8 is disposed, through which the rinsing and regeneration gas 9 can be jetted in periodic cycles to the honeycomb body. The de-fueled fuel gas leaves the reactor through a pipe socket 2 on the side, while dust can accumulate in the floor space, which can be discharged through a discharge nozzle 3 .

Publications under consideration Patent specifications

JP60235634

DE-OS-1542624

EP0360505

DE19721630C1

DE4430645A1

Specialist publications

ALDEN, H .; ESPENÄS, BG; RENSFELT, E .:
Conversion of tar in pyrolysis gas from wood using a fixed dolomite bed, Research in thermochemical Biomass Conversion, 1988

BORN, M .; Berghoff, R .:
Gasification process for waste disposal. Springer-VDI-Verlag, 1998

OLIVARES, A .; AZNAR, MP; CABALLERO, MA; GIL, J .; FRANCES, E .;
CORELLA, J .: Biomass Gasification: Produced Gas Upgrading by In-Bed Use of Dolomite. Ind. Eng. Chem. Res., 36, 1997

ORIO, A .; CORELLA, J .; Narvaez, I .:
Performance of Different Dolomites on Hot Raw Gas Cleaning from Biomass Gasification with Air, Ind. Eng. Chem. Res., 36, 1997

RENSFELT, E .:
Atmospheric CFB gasification. Conference volume 'Gasification and pyrolysis of biomass', Stuttgart, 1997

SIMELL, PA; LEPPÄLAHTI JK; BREDENBERG, JB:
Catalytic purification of tarry fuel gas with carbonate rocks and ferrous materials. FUEL, Vol 71, 1992

SIMELL, PA; KURKELA, E .; STAHLBERG, P .:
Formation and catalytic decomposition of tars from fluidized-bed gasification, Research in thermochemical Biomass Conversion, Vol 1, 1994

THOME-KOZMIENSKY, KJ:
Pyrolysis of waste. EF publishing house, 1985

Other specialist literature

NETWORK. H.:
Combustion and gas production for solid fuels, Resch-Verlag, 1982

HALLGREN, A .:
Theoretical and Engineering Aspects on the Gasification of Biomass, Dissertation, 1996
Handbook of Biomass Downdraft Gasifier Engine Systems, US Department of Energy, 1988

Claims (11)

Device for using gases generated during gasification of biomass for a direct energy conversion, with a gasification unit, into which the biomass to be gasified can be introduced and fuel gases are generated in the supply of a gasification agent, a gas cleaning unit downstream of the gasifier unit, a gas cooling unit following the gas cleaning unit, a dedusting unit (= filter) following the gas cooling unit and one which at least partially converts the energy contained in the cleaned and cooled gases into electrical current, characterized in that the gas cleaning unit has catalytically active material which is directly exposed to the gases emerging from the gasifier unit. Device according to claim 1,
characterized in that the catalytically active material is selected such that the gases emerging from the gasification unit, which contain hydrogen, carbon monoxide, methane, carbon dioxide and water vapor as essential fuel gas components and also higher hydrocarbons (= tars) as by-products, by way of catalytic cleavage can be converted according to the following reaction equations: C _n H _m + n H ₂ O → n CO + (n + m / 2) H ₂ C _n H _m + n CO ₂ → 2n CO + (m / 2) H ₂ With:

C _n H _m

Hydrocarbon compound ~ tars

H ₂ O and CO ₂

Gas components.

Device according to claim 1 or 2,
characterized in that the catalytically active material is composed of one or more catalytically active materials. Device according to one of claims 1 to 3,
characterized in that the gas cleaning unit provides a thermally insulated full-space reactor which has a feed line through which the gases emerging from the gasification unit can be introduced into the full-space reactor, that flow channels are arranged longitudinally in the flow direction of the gases within the full-space reactor, at least on the surfaces of which the catalytically active material is provided, and that a discharge line is provided on the full-space reactor, through which the catalytically split gases emerge from the full-space reactor. Device according to claim 4,
characterized in that the flow channels have honeycomb-like flow cross sections. Device according to claim 4 or 5,
characterized in that upstream or downstream of the flow channels in the flow direction, a cleaning unit is provided for the flow channels, by means of the flushing and cleaning gases, in the form of free jets of oxygen, nitrogen, carbon dioxide or water vapor or a mixture of these gases can be introduced into the flow channels is. Device according to one of claims 1 to 6,
characterized in that the full-space reactor can withstand operating temperatures of 700 to 1000 ° C. Device according to one of claims 1 to 7,
characterized in that the gas cleaning unit provides a gas filter in the manner of a hot gas filter which is placed between the gasifier unit and the catalytically active material, and
that the hot gas filter has a filter medium that consists of a heat-resistant ceramic or metallic material. Device according to one of claims 1 to 8,
characterized in that the carburetor unit and the gas cleaning unit and / or the gas cleaning unit and the gas cooling unit are designed as one structural unit. Device according to one of claims 1 to 9,
characterized in that the gases cleaned by the catalytic cleavage and subsequently cooled and dedusted gases can be fed directly to the energy converting unit. Device according to claims 1 to 10,
characterized in that the energy converting unit is a gas engine, a gas turbine, a fuel cell or a Stirling engine.

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